Temperature responsive device



Feb. 3, 1942. l

u 'TEMPERATURE RESPONSIVE DEVICE Filed April 4, 1940 @bgg mmc@ C. l.`HALL i 3 Sheets-Sheet 1 [LINE/V7' RESISTANCE@ @HHS n HiaAAttor-neg,

REFERENCE Feb. 3, 1942. c. l. HALL 2,271,975" TEQPERATURE RESPONSIVEDEvIcE l Filled Ap'ril 4. 1940 s sheets-sheet 2 Inventor: Chester- I.Hall,

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"CROSS REFERENCE" Feb. 3, 1942. c. l. HALL 4 TEMPERATURE RESPONSIVEDEVICE l "Fi1ed April 4, 1940 3 Sheets-Sheet 3 600 1000 15mm me: oran-:sF

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Patented Feb. 3, 1942 f mums assronsrvs navos chuter l. nali, scnenemay.N. Y., minor to General El New York eetric Company, a corporation ofannue-suon Apen i, me, sensi No. :zam

(ci. :o1-5m C 3 .12 Claims.

This invention relates to temperature responsive devices. and it has forits object the provision of an improved device ci this character andmethod of making it.

This application is a continuation-in-part of my copending application,Serial No. 281,856, illed June 29, 1939, which is assigned' to the sameassignee as this application.

More specifically, this invention contemplates the provision of atemperature responsive device which may be used, for example. to controlan electric circuit in accordance with temperature, the responsivedevice being provided with an element the resistance of' which varieswith temperature, that is. one having, for example. a high initialresistance that is reduced'as the temperature of the element increases.ind this invention contemplates the provision of an improved temperatureresponsive device of this character which is extremely sensitive totemperature changes; which may be operated through a very widetemperature range, and at very high temperatures; one which will provideextremely large variations in resistance with small temperature changes:one that will give constant resistance values and characteristics whenmanufactured and also after long continued service, that is, a controldevice which is reliable and stable in its operation; and one which issimple, rugged, and mechanically strong; and it further contemplates animproved method of making the control device that insures a reliable anduniform product, and which may be manufactured cheaply withcomparatively simple manufacturing methods.

In accordance with this invention, a suitable temperature sensitiveresistance material is highly compacted, and is intimately bonded withits electrodes that are suitably prepared'in accordance with thisinvention to insure the intimate relationship between the highlycompacted resistance material and their surfaces that contact thematerial. One of the electrodes may be in the form of a casing housingthe insulating material, and preferably will be `arranged so that it'maybe placed directly in contact with the medium or body to whosetemperature the device is responsive. In this manner, the time requiredfor the transfer of heat from the body or lmedium to the temperaturesensitive material is 'greatly reduced.

The resistance material in granular form is highly compressed,preferably in relatively short sections, and while in contact with theelectrodes.

` ance material so compact, coherent mass having uniform densitythroughout and having considerable mechanical strength. This mass isbonded to the electrodes so as to be in intimate thermal and electricalcontact with them. For this purpose. the electrodes before the sinteringoperation will have been provided with coatilgls of a flux and an oxideof the electro ng the sintering operation, these coating coal ,ith theresistn eilect the resistance material is sintered into a coherent masswith the electrodes.

The temperature sensitive device forming the subject matter of thisapplication may be employed either as an element of a pyrometer orthermostat, that is either as a device to record temperature or tocontrol temperature. Any suitable means may be used to'determine theresistance of'the device and hence inferentially the temperature towhich it is subjected. By way of example, if the device is connected inseries circuit with a source of potential, the current flow in thecircuit will vary in functional relation to the resistance. Hence, a4current measuring device connected in the circuit may be graduated toread directly in temperature.

Likewise, the device may be used in conjunc- 'tion with control devicesto regulate automatically the temperature to which it is exposed or tocontrol an agent or medium in accordance with that temperature. Suchcontrol devices may be actuated directly or in conjunction with themeasuring devices previously referred to.

For a more complete understanding of this invention, reference should behad to the accompanying drawings in which Fig. l is an elevation of atemperature responsive device arranged in accordance with thisinvention; Fig. 2 is an enlarged fragmentary sectional view of thedevice of Fig. 1; Fig. 3 is a diagrammatic view illustrating theresistance-temperature relationships for various'resistance materialsused as the temperature 'sensitive element; Figs. 4, 5 and 6 areelevations illustrating certain devices used in making the controldevice of Figs. 1 and 2, the elevation in Fig. 4 being in section; Fig.7 illustrates diagrammatlcally a. heating member used to heat-treat thetemperature sensitive element in accordance with this invention; Fig. 8is a diagrammatic representation showing the relationship between theresistance of the control device and time that is effected in one of theheat-treat- It is' suitably heat-treated to sinter it into s. 55

ing steps used in making the control device; Fig. 9 is a view similar toFig. l, but showing a modined form of this invention, and having partsin section; Fig. 10 is an enlarged sectional view 'of the modifiedformof the invention shown in Fig. 9; Figs. 1l, l2 and 13 arediagrammatic views illustrating certain means for modifying theCXDBDSIOB. Mixtures f u 1.1!

sodium silicate 519ml wi out`any copper "oxide, may 'used in differentproportions to obtain different desired characteristic curves andcoemfundamental relationship between temperature 6 cients of expansion;and still other variations and resistance of the control device of thisinvention; and Figs. 14, 15 and i6 are curves showing the changes in thefundamental resistance characteristics of the control device elfected bythe controlling elements shown in Figs. 11, 12 and 13 respectively.

Referring to Figs. l and 2. this invention has been shown in one form inconnection with a temperature control device for controlling the circuitof an electric furnace (not shown). As shown, the control devicecomprises a cartridge III which is provided with a pair of electrodes IIand I2 spaced from each other. The inner electrode II is inthe form of acore. while the outer electrode I2 is in the form of a cylinder. closedat one end, as shown. Interposed between the electrodes and embeddingthe inner end of the electrode II is a mass I3 formed of resistancematerial having a negative temperature coeillcient.

The material of which the inner and outer electrodes II and I2 is mademay-vary widely, the maximum temperature at which the control device isto operate being one of the chief factors to be considered in selectingthe material that will be used; for example, for temperatures rangingbetween zero and 800 F. a metal known as Monel" may be used, while ifthe temperature range should vary between 100 and 1000 F. it ispreferable to use nickel.

The material Il will be chosen in accordance with the characteristictemperature-resistance curve desired, and also so as to provide aninsulating mass having substantially the same thermal coemcient ofexpansion as have the electrodes that will be used. For a particulardesired temperature-resistance curve and where nickel electrodes areused, a mixture of m nesium oxide, sodium silicate and co r oxide Vwi beused Having a ratio 5y weight of .2 of copper oxide to 2.52 of maesiumoxide and 1.17 of cium sili te. The sodium silicate is made up of iiconoxide and sodium oxide, and it is preferable that these materials shallbe in the ratio of approximately l:3.22, although this ratio may bevaried to give erent desirable physi cal characteristics.

Different temperature-resistance characteristice and coemcients ofthermal expansion may be obtained yby varying the proportions of theingredlents used. Generally it is Ipreferable to vary the percentage ofthe copper oxide in the mixture. Fig. 3 illustrates how the resistancecharacteristics will vary with temperature with dinerent ratios ofcopper oxide. Curve a corresponds to the above example where theresistance has a ratio by weight of .25 of copper gmde, to A 2.52 ofmagnesium oxirle and TA? of silicate; curve"b"is`the""curve of a "wherethe ratio by weight of coppergwxide k changed to 1; c where itis changedto 3; and d where it is changed to 6. When the ratio of copper oxideisvaried tocontrglmtne the o vmagnesium oxide to sodium silicate shouldbe substantially constant for the various resistances.

However. the percentages of magnesium oxide, sodium silicate and copperoxide all may be varied to obtain different temperatureqesistancccharmayv be had by substituting zirco aluminum oxide and the like forthe magnesium oxide, an using zinc oxide. nickel oxig chromium oxideand' the like in place of the coppe'r ox e. A wide range oftemperature-resistance characteristic curves, and coefiicients ofexpansion may be obtained by selecting different ones of these materialsand using them in different proportions.

The resistance I3 is highly compacted and the various ingredients of theresistance are sintered to each other and are also intimately bonded tothe outer surfaces of the inner electrode II and to the inner surfacesof the outer electrode I2.

The control device thus far described is made as follows. The innersurface of the outer electo formfawe of the oxide and silicate on the suaces of the electrodes.

The outer electrode I2 is then mounted in a form Il (Fig. 4) havinggreat mechanical strength. This form Il, as shown, is provided with ahole or recess I5 which will have such a diameter that the outerelectrode I2 will have a sliding fit with it. A measured quantity of theresistance material I3 in granular form is then poured into the outerelectrode I2.

acteristics. and to provide dinerent coefncients of "5 It is to beunderstood that it is desirable that the material Il be in the form offine granules that will pass through a 200 mesh screen. Moreover. thegranular ingredients which make up the material Il musi'I be thoroughlymixed. Furthermore. it is desirable that these materials be chemicallypure and anhydrous. Before the granular mixture be used. it ispreferable that it be heated for about 3 hours at around 400 F. in orderto drive oi! any moisture that may have been absorbed by the mixturewhile it is being handled. and preferably it will be introduced into theelectrode I2 while still hot. After the measured quantity ofthe mixturehas been placed with in the outer electrode I2, it is subjected to agreat pressure by means of a suitable plunger. such as the plunger I6shown in Fig. 5. Preferably. the mixture will be compressed at about tentons per square inch. This forms a small tablet I1 in the inner end ofthe electrode I2. as shown in Fig. 4 and as indicated in dotted lines inFig. 2. It will be observed that the lower end of the plunger Il whichcontacts the resistance granules is conical so that the tablet I'I willbe provided with an upper coni- """fcRo'sS REFERENCEshown-inlilg.ti,willbeused. Asshown.this

plunger is 'provided with a passageway il throughout its length: thispassageway receives sembly and the form I4 is provided with an aperture20 through which a suitable instrument (not shown) may be inserted todrive the assembly from the form. f

'Ihe assembly of the two electrodes Il and I2 and the compressedresistance material Il is then placed in a suitable furnace, such as anelectric' furnace, where it is heated for about one hour at atemperature of around 950 I'. It is brought up to this temperature fromroom temperature relatively slowly so that any moisture or water whichmight be contained in.the powder will not generate steam which mightblow out or disturb 4portions of the powder. Preferably. it shouldrequire about one hour to bring the unit up to this temperature of 950F. 'Ihisheatlng operation drives out any moisture which may` have beenpicked up by the resistance material, or which may not have been drivenout by the previous drying out step referred to above.

The assembly of the electrodes and resistance powder maybe heated inthis manner in a tube Il as shown in Fig. 1. This tube has one endclosed and the other end open, and is sumciently long to receive theentire cartridge unit il.

, Preferably, the walls will be made of a suitable high temperatureporcelain material. The tube and cartridge assembly preferably will beheated in a high temperature electric furnace.

,After the assembly has been heated for one hour at 950 F. the energyrateto the furnace is increased so that in a period of about two hours ahigh sintering temperature will be reached. I'his temperature while highshould be well below the melting temperatures of the materials. -l'brthe above specific example having a ratio by weight of .25 of copperoxide to 2.52 of magnesium oxide and 1.47 of sodium silicate a sinteringtemperature of aroundggglgkwill be used. The

' bly is held at temperature for about ten minutes and then is permittedto cool down slowly to atemperature of about 1100:. F. where 1t is nelefor about 1s hours, af erw@ it n permutedweqol.: u

One end o`f tle furnace 2l is left open during the above-describedheating steps so as to expose the resistance material il within theouter electrode i2 to a normal air atmosphere. while the outer surfacesof the electrode I2 are in an atmosphere substantially free from oxygen.It is important that the contents of the electrode i! be thus exposed toair, particularly where one Manganime tustfthseeformcuoshssatendencytoreduceto it te feeparticlesofthegrsnuls'mixturesothatin the resistance material It isformed intoa medium high temperature and for a relatively long period oftime.

an air atmosphere. The same furnace 2| may be yused for mixture of theabove example, the assembly is aged at a temperature of around 1000 to1100 and for a period of about 40 to 50 hours. The

aging temperature is selected so as to be some-- what higher than theultimate temperature at whiclr the element is to be operated. While thev miiliamperes. The aging process causes all of vFil. 8.

the copper oxide in the form of CuO, which has not reverted to CuOs. togo back to this stable form. This stablizes the resistance. 'nie effectof this aging treatment is shown graphically in Here the resistance atthe end of the nring is likely. to be higher than the stabilizedresistance. as shown by the curve, but after about40to50hoursofagingitwilldropdownand will become stable due to theconversion of the copper oxide from the form CuO to CuOs. Moreover. Ihave found that the aging process greatly improves the Joint or bondbetween the electrodes and the resistance mass. i

The assembly after "aging is then assembled with an extension tube 22which is used to support the cartridge Il ih assembled relation with themedium whose 'temperature is to be controlled, and which tube may beformedof any suitable material. such as steel. Por example, if thecontrol device is to be'used to control the temperature of an electricfurnace. the tube l! willbepassedthroughthefurnacewallsoasto hold thecartridge Il in position to be immersed in the furnace atmosphere. Thelength of the supporting tube Il will depend. of course, upon theparticular application of the control element Il. Preferably, the tube22 will be threaded on the electrode i2, as shown, the electrode andtube having relatively fine inferfitting threads. The threaded jointbetween the electrode and tube will be sealed by a suitable hightemperature cement which is placed on the threads before they arethreaded together..

A suitable lead- 23. which preferably will be formed of nickel. isbrazed to the inner electrode of the ingredients is copper' oxide,because in 7g I2 and extends outwardly through the tube 22. 'Ihis leadis provided with a covering 24 of a suitw XANHNI able electricallyinsulating material, such as asbestos.

I'he outer end of the tube 22, that is its righthand end as viewed inFigs. l and 2 is closed by means of an electrically insulating terminalblock 26 which, as shown, is fitted over this end `like a cap. The blockis made of any suitable material. such as a suitable asbestos board.This terminal block is provided with an aperture 2t through which thelead 2l is passed and it carries a terminal 2l (Fig. 1) to which thelead is brazed. The terminal block 25 also carries a terminal 2l towhich the lead 29 is electrically connected. This lead 29 is directedthrough an aperture I0 provided for it in the terminal block and it iswelded, as shown. to the outer surface of the tube 22, the tube 22, ofcourse, constituting a continuation of the outer electrode i2.

The terminal block is secured by means of a set screw 30a; and the Jointbetween the block 25 and the outer surface of the tube 22 and betweenthe inner walls of the channel 26 and the lead 23 are covered with asuitable electrically insulating sealing cement, such as a suitablealkyd resin.

In the form of the invention shown in Figs. 9 and 10, the cartridge Ilis provided with inner and outer electrodes 32 and 33 which are both inthe form of cylinders closed at one end, as shown.

Here the two electrodes are separated by a mass 2l formed of theresistance material having a negative temperature coefficient and whichma terial will be the same as the material I3 of the first form.

The cartridge 3l is made in substantially the same way as the cartridgeI0. Thus, the `inner walls of the cuter electrode and the outer walls ofthe inner are provided with coatings comprising the oxides of theelectrode walls and a suitable flux, such as sodium silicate; theresistance material 34 is prepared in the same way as the material i3;the electrode 3| is placed in a form and a tablet of the resistancemat'erial, similarto the tablet I1, is formed in its inner end; theinner electrode is inserted with its tapered end fitted in the tablet;and the rest of the resistance material 3l is then compressed intoplace. The assembly is then given the treatments described in connectionwith the first form, whereby acoherent mass of sintered resistancematerial 34 is lprovided embedding the inner end of the electrode 32 andintegrally united with the surfaces of the electrodes which it contacts.Here, a supporting steel tube 35 is secured t0 the outer end of theelectrode 33- In this case the tube 25 is welded to the electrode. Aninsulated lead 26 has its inner conducting end welded to the innerelectrode 32 while its outer end is passed through a conducting bolt 31which has a central passageway, as shown, for receiving the lead. Thisouter end of the lead is soldered to the outer end of the stud 31.'I'his stud 31 passes through an insulating terminal Abloclr or head 28formed of any suitable electrically insulating material, such asasbestos board. As shown, this member 38 has a centrally arrangedaperture through which the ably will be sealedto the inner walls of -thetube 1o l5 and tothe stud Il by means of a suitable electricallyinsulating celrient,- such as alkyd resin. l t

It will be understood that for my given temperature responsive cartridgehaving a particular temperature sensitive resistance the cartridge willhave a fundamental temperature-resistance relationship. That is, theresistance of theelement wilidrop rapidly with temperature lncrease.along a nxed curve, which is incapable of modification after thecartridge has once been produced since the slope of the curve and theactual values of the coordinates are dependent entirely upon the qualityand kind. of resistance materialused and the process through which ithas been carried. For example, with a specific cartridge, the resistanceof the element will vary with temperature as shown by the solid curve inFig. 14. At times, it is desirable to modify the shape of this curve andthis may be accomplished by suitable controlling resistances inserted inthe controlled circuit in which the controlling cartridae is placed.Referring to Fig. ll, the rechanges. Moreover, the resistance mass isbond -on the fundamental sistance of the cartridge is indicated Ri- If aseries resistance Rz be placed in the controlled circuit, as showndiagrammatically in Fig. ll, the high temperature end of the curve aloneis affected, as indicated in dotted lines in Fig. 14. This is becauseafixed series resistance becomes lproportionately a lower ratio of thetotal resistance as the temperature is reduced.

On the other hand, a parallel resistance will affect only the cold endof the curve since its ratio of effectiveness is entirely negligiblewhen' the control element resistance Ri is low. Fig. 12 shows aresistance R: connected in parallel with the resistance Ri, and Fig. 15shows in dotted lines the eiiect of the addition of this resistancetemperature-resistance curve.

In Fig. 13 both a series resistance R5 and a parallel resistance R4 areused. In this case one resistance is effective at one end of the curveand the other at the other end so as to modify` the slope of the curvethroughout, as shown in Fig. 16.

It will be understood, of course, that the effectiveness of thecontrolling resistances may be varied as desired by any suitableadjusting means so that the slope of the fundamental characteristiccurve 'for any particular cartridge elemen may be varied.

It will be observed that I have provided a temperature control elementwhich is extremely sensitive to temperature changes. 'I'he sensitiveresistance is in intimate thermal relation with its outer electrodewhich functions as a casing to bring it into contact directly with themedium whose temperature is to be controlled; the particles forming theresistance sensitive element are compacted under a tremendous pressureand are sintered so as to form a compact, coherent mass. Thiscoherentcompacted body is bonded and substantially integrally unitedwith the surfaces of the outer electrode -which is immersed in 'themedium whose temperature is to be controlled which insures a minimumtime lag in the response of the'control device to temperature ed withthe outer electrode land also with the inner electrode to eil'ect a verygood electrical connection between these members. In addition, the unitis mechanically strong and will withstand considerable abusage before itwill be damaged, far more abusage than will be encountered in itscontrolling applications: it is stable and durable: and is physicallysmall so that its range of application is materially extended. It willalso be observed in view of the foregoing description .of the method ofmaking this unit that relatively simple manufacturing steps are used. Inaddition to this, the construction of the element in its various partsand the method whereby these While I have shown particular embodimentsof my invention, it will be understood. of course. that I do not wish tobe limited thereto since many modifications may be made, and I,therefore, contemplate by the appended claims to cover any suchmodifications as tall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A temperature responsive device comprising a tubular metallicelectrode closed at one end, a second metallic electrode inserted insaid tubular electrode and spaced from its walls. and a temperaturesensitive resistance material within said tubular electrode embeddingthe inner end of said second electrode formed of a preselected mixtureof granular magnesium oxide, sodium silicate and copper oxide. thegranular particles of said mixture being highly compressed and sinteredinto a coherent mass and bonded intimately with the surfaces of said twoelectrodes.

-2. A temperature sensitive device comprising spaced metallicelectrodes, a sintered mass of temperature sensitive granular resistancematerial between surfaces of said electrodes, said surfaces beingprovided with iiuxed coatings intimately bonded with said surfaces andalso sintered into a coherent mass with said sintered granularresistance material.

3. A temperature responsive device comprising a tubular metallicelectrode closed at one end, a second metallic electrode inserted insaid tubular electrode and spaced from its walls. granular resistancematerial within said tubular electrode embedding the 'inner end portionof said second electrode sintered into a coherent mass that is bondedintimately with surfaces of said electrodes. a tubular supportingextension supporting said outer electrode. a lead connected to saidinner electrode extending through said tubular extension, a leadconnected to said tubular extension, an insulating member closing saidtubular extension and having apertures through which said leads pass,and means for sealing the joints between said electrode and saidextension.

and between said extension and said closing member, and also for sealingsaid closing member to said lead that extends from said inner electrode.

4. The method of making a temperature responsive device which comprisesinserting a metallic electrode into a tubular metallic electrode thathas one end closed so that the ilrstnamed electrode is in spacedrelation with the 4walls of the latter, inserting granular temperaturesensitive resistance material inw said tubular electrode in relativelysmall quantities at a time and highly compressing each quantity of thematerial after it has been added and before the next quantity has beenadded, and then nring at a high temperature to sinte'r said granularresistance material.

5. The method of making a temperature responsive device having a pair ofspaced electrodes joined by a temperature sensitive resistance materialformed of magnesium oxide. sodium silicate, and copper oxide whichcomprises mixing granules of said materials together. placing thembetween said electrodes. compressing said granules to highly compactthem while in contact with said electrodes, heating said compactedgranules slowly until a temperature of around 950 Il'. is reached inabout one hour. holding said temperature for about one hour, increasinglance material formed of magnesium oxide, so`

dium silicate. and copper oxide which comprises mixing granules of saidmaterials together, heating said granules at a temperature of aroundy400 F. for about three hours, placing said gran'- ules whileheatedbetween said electrodes, compressing said granules Vto highly compactthem while in contact with said electrodes. then gradually raising thetemperature of said compacted granules in about onelhour to atemperature of about 950 F. and holding said temperature for about onehour, increasing the temperature of said compacted granules so that inabout two hours it reaches a sintering temperature of around 1975 F. andholding said temperature for around ten minutes. and then permittingsaid insulating material to cool to a temperature of around 110,0 Il'.and holding said temperature for about sixteen hours. v

7. The method of making a temperature responsive device having spacedmetallic electrodes and a temperature responsive element formed of asintered granular temperature sensitive resistance material between themcomprising forming on the surfaces of said electrodes that shall contactsaid resistance material coatings consisting of a mixture of a metallicoxide and a iiux that are capable of being sintered to said granularresistance material. compressing granules of said resistance materialinto a dense mass in contact with said coatings, and then sintering saidgranules to cause them to coalesce with each other A and with saidcoatings.

A ings 8. The method of making a temperature responsive device havingspaced metallic electrodes and a temperature responsive element formedof a temperature sensitive resistance material between them comprisingheating surfaces of said 9..'I'he method of making a temperature re- 75sponsive device having spaced electrodes and a temperature sensitiveresistance element joining 4 said electrode which comprises forming atubular electrode, and also a second lelectrode adapted -to be insertedin said first electrode in spaced relationwith its walls, inserting aquantity of said resistance material in said first electrode, highlycompressing said material to form a relativelyl of pressure stepsbetween said electrodes. and

then highly heating the assembly of electrodes and resistance materialso as to forma substantially coherent mass of said resistance material.

10. The method of making a temperature responsive device having spacedelectrodes and a temperature sensitive resistance element Joining saidelectrodes which comprises forming a ltubular electrode and a secondelectrode adapted to be inserted in said first electrode in spacedrelation with its walls. inserting a quantity of a mixture loi magnesiumoxide, sodium silicate 'and copper oxide granules in predeterminedproportions in said iirst electrode and highly compact.- ing saidgranules in the spaces between said electrodes. and highly heating theassembly o! velectrodes and granules to sinter the granules into acoherent mass while maintaining a non-oxidizing atmosphere outside o!said assembly and an oxidizing atmosphere within said first electrode.

11. The method o! making a temperature re-A sponsive device having apair o! spaced electrodes Joined by a temperature sensitive resistancematerial formed o! magnesium oxide. sodium silicate. and copper oxidewhich comprises mixing granules of said materials together, placing thembetween said electrodes. compressing said granules to highly compactthem while in contact with, said electrodes, heating said compactedgranules slowlyvuntil a temperature of around 950 F. is reached in aboutone hour. holding said temperature for about one hour, increasing saidtemperature in about two hours to around 1915 F. and holding saidtemperature for around ten minutes, and then permitting said granules tocool down to a temperature of around 1100" F. and holding it at thistemperature for around sixteen hours, and then aging" said resistancematerial from around forty to iifty hours at a temperature of around1000 to 1100 F.

12. The method ot making a temperature responsive device having a pairoi.' spaced electrodes Joined by a temperature sensitive resistancematerial formed oi' magnesium oxide, sodium silicate, and copper oxidewhich comprises mixing granules o! said materials together, placing thembetween said electrodes. compressing said granules to highly compactthem while in contact with said electrodes. heating said compactedgranules to sinter them into a coherent mass. and

CHESTER I. HALL.

f caimrrcirs or consorten.

Patent No. 2,271,9Y5.v

crmsrsn I. HALL. f

^ February 5, 19112.

Itis hereby certified thaterror'appears 1ni the printed. specificationofthe above numbered patent requiring correction as follows: Rage'Z,first column, 11ne 555lt, for "characteristice" readcharacteristics-Qg'page il,

second column, line 1|., forv "my'i 'rnd 'W....

page 6, 'first column, -line 2, claim 9, for "electrode" readl-e1eci:ro'iesv'; artiA 'that the said Letters Patentshould be read withthis correction that the smemiey conform to the record of the case in.the Patent Office. s

signed and sealed this alim dey or web', A. o. 19112. f

` (seall Henry Ven lirsdale, Acting Commissioner of Patents.

a y cEmFIcATE'oF conmcnon. l Patent No. 2,271,975. February 5, l9l|.2..I

CHESTER I. HALI. o

Itis hereby certified tknterrorappears in the printed specificationofthe above numbered patent Arequiring correction as follows:Rage'2,.first column,V 1ine 5551|., for "characteristics" read--characteristice-;fpage h., second column, line h, for "my". fread--any--glpage 6, first column, -line 2, claim 9, for l"electrode" read`--electrode's--g and. that the said Lettere Patentshould be read withthis correction that the eamemay conform to `the record of the caseinthe Patent Office.

d signed and sealed this aim; day or nag-ch, A. D. 19142.

Henry Van Arsdale, {Seal} Acting Conmissioner of Patents.

